How to format floating number values for Garmin Connect statistics properly?

I have a datafield that generates a fit session value. Purpose is to display the value in garmin connect in the "statistics" tab:

FitContributor.DATA_TYPE_FLOAT,

            {
                :mesgType => FitContributor.MESG_TYPE_SESSION,
                :units => WatchUi.loadResource($.Rez.Strings.ActivityEnergyLabel) as String
}

In ressources.xml i have this:

<fitField id="5" displayInActivitySummary="true" sortOrder="4" precision="1" dataLabel="@Strings.ActivityEnergy" unitLabel="@Strings.ActivityEnergyLabel"/>


It works, value and unit are shown. But sometimes i see bad formatting:

a) 0,1 is displayed as ,1 -> missing leading zero
b) Floats are sometimes displayed like 0,1344634412 -> to many digits
How to control the field format in garmin connect?